1. Field of the Invention
The present invention relates to a method and circuitry for safely regulating the charge and discharge cycles of implantable grade, rechargeable power sources, utilizing inductively coupled radio frequency energy. Patient safety and power source longevity are vastly improved by the method and circuitry of the system of the present invention. Such safety and longevity are obtained by the steps of: (1) measuring and recording, each charge/discharge cycle, to obtain the corrected capacity of the power source in order to calculate and display, upon interrogation, the remaining operating time of the implanted device, (2) providing within the implanted medical device circuitry for disconnecting the power source upon reaching a pre-selected low voltage in order to prevent deep-discharging the power source below safe limits, (3) providing circuitry for using variable constant current charge rates, (4) providing circuitry for switching to constant voltage to top-off the power source at the completion of the charge cycle, in order to prevent overcharging beyond safe limits, (5) providing within the implanted medical device circuitry for disconnecting the charging circuit from the power source upon the power source reaching a preselected high voltage level, (6) providing circuitry for full-time RF powered operation, in case of failure of the internal power source or for operation of the implanted medical device requiring extremely high power consumption (rather than being powered from the internal power source of the implanted device), (7) providing circuitry for transmitting to a remote receiver, via a telephone link, critical data that can be used by the physician and/or the device manufacturer to assess the performance and condition of the rechargeable power source and the Implantable Medical Device, and (8) providing circuitry for transmitting to the implantable medical device, via a telephone link, new operation parameter value(s).
2. Description of the Prior Art
A number of new, state-of-the-art, implantable medical devices are powered by a rechargeable electrical power source, such as a small volume, large value capacitor (known as a such as a small volume, large value capacitor (known as a Super-capacitor), or a rechargeable electrochemical cell. These power sources need to be periodically recharged by an external Radio Frequency (RF) Transmitter via inductive coupling in a manner known in the art.
Each type of power source has a different charge and discharge methodology which must be faithfully followed to prevent permanent damage to the power source. In the prior art, the charge/discharge methodology has been factory preset via a specific hardware circuitry, suitable only for the specific power source used to power the implantable device. Furthermore, the prior art circuitry is incapable of properly regulating the charge/discharge cycles of new implantable-grade power sources, such as a Lithium-Ion cell battery.
Heretofore various battery power source charging systems have been proposed. Examples of some of these previously proposed systems are disclosed in the following U.S. patents:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 5,411,537 Munshi et al. 5,631,537 Armstrong 5,670,862 Lewyn 5,675,235 Nagai 5,764,030 Gaza 5,811,959 Kejha 5,818,199 Beard 5,880,576 Nagai ______________________________________